Pressure sensitive adhesive labels are generally provided with a releasable backing known as a backing layer, release layer or release liner. The backing protects the adhesive surface of the label from contamination by dust, debris, moisture and other contaminants until the label is ready for use. It is important that the backing is easily releasable from the label so that the label does not tear when separated from the backing. Easy release is also needed so that the adhesive layer of the label remains intact during separation, enabling maximum adhesion of the label when applied to a subsequent surface.
Silicone coatings on paper products are well known as suitable materials for release liners, release backings and other low surface energy surfaces. Unfortunately, such materials are not suitable as moisture and water barrier materials, and are relatively expensive due to the thickness required for such materials to be commercially durable. Furthermore, silicone-coated paper products have a rough topography due to the fibrous and porous nature of the paper. The topography of the paper tends to be transferred to and adversely affects the smoothness of the label adhered to it. This is particularly troublesome when paper release backings are used for transparent labels having adhesive layers which tend to pick up the topography of the backing. When the rough topography of the backing is transferred to the adhesive layer of a transparent label, clarity of the adhesive layer and thus the label is diminished. A need therefor exists for an extremely smooth backing material which will not cause the transfer of a rough topography to the adhesive layer of a transparent label.
Other problems with the use of silicone-coated paper backing and liner materials is the tendency of such materials to rip or tear during a diecutting operation. A need exists for a backing and liner material which can be neatly cut by a diecutting press so as to achieve a finished form having smooth edges.
Release-coated surfaces are also desirable for containers, trays and support sheets which contact foodstuffs, and for drums, tubes and containers for tacky or sticky industrial compounds. Complete release of foodstuffs and industrial compounds from such surfaces is essential to minimizing waste of such products. Complete release of foodstuffs from container surfaces also preserves the appearance of the foodstuff and thus provides an aesthetically pleasing presentation of the product. For example, it would be desirable to provide a release-coated surface on a pizza box or pizza tray insert so that melted cheese overflowing from a slice of pizza will not stick to the box or tray. When melted cheese from a slice of pizza flows onto the surface of existing cardboard pizza boxes, the cheese sticks to the box and pulls more toppings off the slice as it is lifted from the box. A need therefore exists for food containers, support sheets and trays provided with release coatings which prevent sticking of foodstuffs to the surfaces thereof.
Likewise, a need exists for an industrial composition or compound container such as a drum or tube having a release coating thereon which prevents sticky or tacky industrial compounds from sticking to the container.
Coated paper liners are also known for food containers and industrial compound containers, and are desirable in that they offer good printability and stiffness. Unfortunately, coated paper liners require sufficient thickness to provide satisfactory tear resistance and they suffer from the undesirable properties of moisture scavenging and curling. Moisture scavenging results in the absorption of water content from foodstuffs and industrial compounds in contact with the liner, thereby adversely affecting the quality of the contained foodstuff or industrial compound and the structural stability of the container.
Certain polymeric compositions provide good moisture barrier properties and tear resistance, but offer poor printability and stiffness. Polymeric liners may also be dimensionally unstable for many applications. U.S. Pat. No. 5,244,702 discloses a paper-plastic laminate sheeting which can be used for manufacturing grocery bags and envelopes. The patent does not suggest, however, that the laminate could be used as a release backing. The plastic layer may comprise a film of polypropylene, polyethylene, nylon or polyester. To avoid diminishing the reinforcing characteristics of the film, the patent teaches using a water-based adhesive, and not a hot melt adhesive, for laminating the film to a paper layer. To render the inner surface of the film more receptive to the water-based adhesive, the patent teaches first subjecting the film surface to an ionizing treatment to increase the surface energy of the film surface.
It has been found that ionization treatments, unless conducted at extremely low power, can deleteriously affect and even destroy silicone coatings on a thin polymeric film. Destruction of silicone coatings on thin polymeric films may occur even when the opposite surface of the film is the only surface exposed to the ionization treatment.
The present invention provides a backing and liner material having a silicone release surface. The multi-layered products of the present invention exhibit excellent release, printability, stiffness, tear resistance, and dimensional stability together with moisture barrier properties. The present invention provides a method of producing such backing and liner materials in a thin structure and at a continuous high production rate without deleteriously affecting the silicone release surface. The printability and stiffness of a coated paper release structure and the tear resistance and moisture barrier properties of a polymeric liner are achieved while avoiding curling problems and swelling due to absorption of water into a paper layer.
The highly smooth silicone-coated polymeric surface eliminates problematic transfer of a rough topography to label adhesives. The present backing and liner materials may be substantially thinner, e.g., thinner than about 60% as thick, yet at least as strong as silicone-coated paper materials. In addition, the materials of the present invention possess a smooth surface for diecutting which leads to precise cutting of forms with a minimal risk of material ripping or tearing.